The present invention relates to an outer surface sheet for absorbent articles, such as diapers, incontinence protectors or sanitary napkins, comprising a central part and two side parts of inelastic materials, each of said parts having two longitudinal edge portions and adjacent longitudinal edge portions of the central part and the respective side part are mutually overlapping each other; and further comprising a barrier flap extending along at least a part of each of the longitudinal edge portions of the central part
The outer surface sheets of absorbent articles of the aforementioned kind will often include so-called barrier flaps on that side of the article which lies proximal to the wearer""s body in use. The prime purpose of the barrier flaps is to prevent liquid from running over the upper side of the surface sheet and out to the edges of the absorbent article. The flaps also form together with the surface sheet a basin-shaped cavity in which discharged liquid is stored temporarily before the absorbent body has been able to absorb the liquid discharged. This temporary storage space is particularly important with regard to incontinence protectors for adult persons, since the volume of liquid that is discharged onto such a product at one and the same time can be relatively large. In order to ensure that the liquid stored temporarily in this storage space will not leak from the article, it is necessary for the barrier flaps to lie sealingly against the body of the person wearing an absorbent article that includes barrier flaps on its outer surface sheet. Barrier flaps are often comprised of elongated pieces of inelastic material that are made elastic along one longitudinal edge part with the aid of pretensioned elastic threads. Such flaps are fastened to the outer surface sheet with the elastic threads in a stretched state. When these elastic threads are then allowed to relax, the flaps will take an upstanding position relative to the plane of the surface sheet. One problem with flaps of this nature is that the inelastic material in the flaps will pucker as the elastic threads contract. This puckering, or gathering, of the inelastic material means that the puckered longitudinal edges of the flaps will not seal effectively against the wearer""s body when an article that includes an outer surface sheet on which such flaps are provided is worn.
It is known from Applicant""s Swedish Patent Application No. 9700694-4, filed Feb. 27, 1997, to produce barrier flaps from elastic band material that has a generally smooth abutment surface in both a stretched and relaxed state. One problem encountered with the use of flaps comprised of elastic material is the difficulty experienced in fastening the flaps to the outer surface sheet. This problem has been solved in the aforesaid Swedish Patent Application by using a three-ply film that comprises two polypropylene outer layers and an intermediate layer of elastic film.
EP-A1-0 625 346 discloses a surface sheet according to the introductory part of the description.
An object of the present invention is to provide an outer surface sheet for absorbent articles that includes elastic barrier flaps which are fastened to the outer sheet in a manner such as to enable the use of flaps that consist solely of elastic material. Another object of the invention is to provide such a surface sheet of flexible construction that can be produced in a cost-effective manner without complicating the process of manufacturing the absorbent articles in which the outer surface sheet shall be included.
These objects are achieved with an outer surface sheet according to the introductory part of the description characterised in that the barrier flaps each is comprised of a strip of elastic material having two long edge portions and two end edge portions, wherein one of the long edge portions of each of said strips is inserted between the overlapping longitudinal edge portions of the coal part and respective side part and firmly secured therebetween. Because the elastic barrier flaps are fastened between two inelastic materials, it is easy to produce a secure attachment of the barrier flaps, regardless of whether the flaps are glued or welded in place. Furthermore, the division of the outer surface sheet into separate parts enables the outer sheet to be given a flexible construction by virtue of the fact that the different parts of said sheet may be comprised of different materials.
In one preferred embodiment of the invention, that longitudinal part of the strip which lies between the mutually overlapping longitudinal edge parts of the surface sheet parts is fastened to each of said overlapping parts.
According to a more preferred embodiment of the invention, the surface sheet parts are made of a heat-weldable material and the mutually overlapping longitudinal edge parts of the surface sheet parts are joined together by ultrasound welding or heat welding. The overlapping edge portions of the surface sheet parts are joined together through the longitudinal edge part of the stretched elastic strip sandwiched therebetween. The surface sheet will preferably comprise three separate longitudinal parts, two side parts and a central part, wherein at least the central part will comprise a liquid permeable material, and a barrier flap will extend along the two long edges of said central part. In one variant, the two side parts of the surface sheet are comprised of liquid impervious material and the mutually overlapping longitudinal edge portions of the side parts are placed on top of respective longitudinal edge portions of the central part. Each barrier flap is preferably comprised of a strip of elastic plastic film and tapers or narrows in a direction towards its end parts. Alternatively, the barrier flaps may taper from their end parts towards their centre part.
In one variant, at least one barrier flap extends in the transversal direction of the outer surface sheet.